Thy hydroxylation of diphenylhydantoin by dog liver microsomes will be studied. As a model of the antiepileptic ketogenic diet, ketosis will be produced in mice by feeding a diet containing a high percentage of medium chain triglycerides. Intracellular pH (pHi) of brain will be derived from the distribution of 5,5-dimethyl-2,4-oxazolidinedione (DMO). The toxicity of allopurinol in combination with 6-mercaptopurine will be studied in mice with observations of mortality and depression of the leukocyte count. Purification of dihydropyrimidinase will continue. Further studies will be made of the structural requirements for a compound to be a substrate of the enzyme. Possible homolytic fission of the C-Br bond in halothane will be investigated.